The present invention relates to an apparatus and method for qualifying a chemical mechanical planarization process. More particularly, the present invention relates to an apparatus and method for qualifying a polishing pad used in the chemical mechanical planarization of semiconductor wafers.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected unevenness in the wafer surface. This sensitivity is accentuated with the current drive toward smaller, more highly integrated circuit designs. Semiconductor devices are also commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on a semiconductor wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that is preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized. In some CMP systems, a polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. In other CMP systems, a fixed abrasive pad is used to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
CMP systems using a polishing fluid or a fixed abrasive often undergo pad wear studies for simulating extended patterned wafer runs. These pad wear studies are often necessary in order to bring a new process into production. In order to conduct these pad wear studies, hundreds of patterned semiconductor wafers are often required for process qualification marathons with a single structure. These hundreds of semiconductor wafers cost a considerable amount of money to manufacture and develop. Accordingly, further development of an apparatus and method for qualifying a chemical mechanical planarization process, and more specifically, for qualifying a polishing pad used in the chemical mechanical planarization of semiconductor wafers, is necessary in order to decrease the costs of pad wear studies, which in turn decreases the costs of bringing new CMP processes into production and decreases the cost of CMP process development.
According to a first aspect of the present invention, an apparatus for qualifying a polishing pad used in chemical mechanical planarization of semiconductor wafers is provided. The apparatus includes at least one qualifying member including at least one collimated hole structure, wherein the collimated hole structure forms multiple channels within the qualifying member. In one embodiment, the qualifying member includes a material selected from the group consisting of borosilicate glass, soda lime glass, high-lead glass, and silicon oxide. In another embodiment, each channel within each collimated hole structure has a width of between about 3 microns and about 100 microns.
According to another aspect of the present invention, a method for qualifying a polishing pad used in chemical mechanical planarization of semiconductor wafers is provided. The method includes providing at least one qualifying member formed with at least one capillary tube array, wherein the capillary tube array forms multiple channels within the qualifying member, pressing the qualifying member against the polishing pad, and moving the qualifying member along the polishing pad along a trajectory to simulate the polishing of a semiconductor wafer. In one embodiment, the polishing pad contains an amount of slurry. In one embodiment, the polishing pad includes a fixed abrasive.